Due to the increasing awareness to climate relevant emissions a lot of effort is undertaken to minimize the emission of carbon dioxide, which is thought to be one of the most relevant reasons for the increase of the world's temperature respectively the greenhouse effect. Latest developments led to cogeneration cycles having zero emission and a higher efficiency. Within this cycle fossil fuels are burned with pure oxygen, which enables the separation of the carbon dioxide, generated during the oxidation, in a cost effective way by condensation of the H2O-fraction of the combustion gas. The increased cycle efficiencies compensate at least partly the efforts for the supply of pure oxygen undertaken in an upstream air separation module. This cycle becomes a zero emission cycle if the separated carbon dioxide is stored at an adequate location.
Basically these cycles consist of a so called closed Brayton Cycle operated at a high temperature combined with a low temperature Rankine Cycle. Typically the Brayton Cycle consists of compressors, a combustion chamber and a high temperature gas turbine. Often a Rankine Cycle consists of a steam turbine, a condenser and a steam generator. The steam generator might be a heat recovery steam generator. The turbine can be a one casing turbine or a combination of high-, intermediate- or low-pressure turbines. Preferably the fuel is natural gas or other hydro-carbon based fuel gas together with a nearly stochiometric mass flow of oxygen, which is supplied to a combustion chamber respectively burner, preferably operated at a pressure of 20 bar-60 bar depending on the chosen design parameters for the Brayton cycle, mainly turbine inlet temperature, turbine cooling concept and low pressure compressor inlet temperature. The high temperature turbine is therefore operated at a temperature of up to 1600° C. and the turbine cooling system utilizes the working medium from the compressor which is mainly a mixture of carbon dioxide and water as coolant. The relatively cool working medium from the compressor is also utilized as cooling medium for the burners respectively the combustion chamber and all other parts which are exposed to the high temperature from the combustion. After expansion in the Brayton cycle gas turbine the hot exhaust gas is cooled in a downstream heat recovery steam generator vaporising water and superheating steam for a Rankine cycle high pressure steam turbine.